John Bluck May 2, 2002
NASA Ames Research Center, Moffett Field, Calif.
Phone: 650/604-5026 or 650/604-9000
E-mail: jbluck@mail.arc.nasa.gov
RELEASE: 02-55AR
NASA TO TEST MICROWAVE EFFECTS ON PLANT GROWTH
Microwaves derived from solar power and transmitted by orbiting satellites to
electric power stations on Earth may someday enable U.S. energy self-sufficiency,
but is this method safe for local plant life?
NASA scientists are about to test that hypothesis by evaluating the effects of
continuously beaming weak microwaves on alfalfa plants during laboratory tests.
"One of our main questions is how organisms will respond to sustained microwave
exposure because the beam from space will be on all the time," said scientist Jay
Skiles of NASA Ames Research Center in California's Silicon Valley. Skiles has
designed a series of experiments to test the effects of weak microwave
illumination on plants at 2.45 GHz frequency. "We expect that the microwave
intensity at ground level will be about a million times less than that in a typical
microwave oven."
"Our hypothesis is that plants exposed to microwaves will be no different from
those plants that are not exposed to microwaves," Skiles said. He now is conducting
a prototype experiment in which he illuminates alfalfa plants with low-power
microwaves. "The experiment is designed so that the only variable to which the
plants are subjected is microwave exposure," he explained.
The space solar power concept envisioned by some engineers requires putting
satellites into a geosynchronous orbit at an altitude of 22,300 miles (40,140
kilometers) over the equator. In such an orbit, satellites revolve around the Earth
at the same speed as the planet rotates, causing the satellites to appear to 'hover'
over the same point on the ground below. And at that altitude, they are
continuously in sunlight. Solar cells on the satellites would change energy from
sunshine into electricity. A satellite system would convert the electricity into
microwaves and beam them to receiving antennae on the Earth's surface. There,
systems would convert the microwave energy back into electricity and feed it into
the nation's power grid.
Microwaves are a small part of the electromagnetic spectrum that includes energy
frequencies from x-rays to visible light and radio waves. "These microwaves are in
the radio frequency range, at the same frequencies at which many cell phone
services operate," according to Skiles.
During his current prototype experiment, Skiles broadcasts microwaves over a tray
of alfalfa plants in a laboratory. The microwaves reflect onto the test plants. At
the same time, nearby 'control plants' are not subjected to microwaves. A 'control'
in a scientific experiment is something used as a standard for comparison.
Both the test plants and the control plants are subjected to the same temperature
and lighting regime, and they are grown in the same size pots in the same kind of
potting mix.
Skiles is measuring plant gas exchange and leaf chlorophyll concentration. "Also
measured are gross plant variables, such as stem length and overall vigor," he said.
"This prototype experiment will provide preliminary results based on a 14-hour
artificial day and constant temperature." Skiles also is preparing to conduct a
longer, 6-month experiment in a rooftop greenhouse at NASA Ames starting in late
spring.
"We are going to duplicate the prototype experiment in natural sunlight, and we will
have night and day temperature changes that will give us more realistic
environmental values," he said. "Alfalfa begins to flower in late September, when we
begin to get shorter days in the Northern Hemisphere, and we will end the
experiment then when the plants are getting ready to winter."
"Nobody has accomplished 2.4 GHz sustained microwave plant-illumination
experiments before, to the best of our knowledge," he said. Skiles chose to test
alfalfa because it is an important crop that animals and people eat. Alfalfa also is
representative of a broad class of economically important plants, he added.
Skiles said he is planning additional, longer experiments to test a variety of plants
under various conditions. "Long-duration mixes of plant species experiments as well
as testing single plant species for response to microwaves under stressful
conditions, including plants from a desert ecosystem, will be future tests," he said.
In 1968, Peter Glaser first described the concept of space solar power in an article,
'Power from the Sun: Its Future,' which appeared in the journal Science. "In the late
60's, the science, engineering and technology available made the implementation of
space solar power infeasible," Skiles said.
"Recently, the National Research Council, an arm of the National Academy of
Sciences, in a publication called, 'Laying the Foundation for Space Solar Power: an
Assessment of NASA's Space Solar Power Investment Strategy,' gave a qualified
go-ahead for initial space solar power technology research and development. In
prior assessments, the NRC had indicated that it was premature to pursue this field
of R&D," Skiles said.
The National Academy of Sciences qualified its recommendation that a space solar
power project is feasible by stating that NASA should partner with other
government agencies such as the Department of Energy, Skiles said. "This effort
could be important for national security because space solar power provides one
more option that might enable energy independence in the future," he said. The
NASA Glenn Research Center, Cleveland, Ohio, manages the space power project.
NASA's Human Exploration and Development of Space strategic enterprise,
Washington, D.C., directs the space solar power investigations for the agency.
High-resolution images in 'publication format' are available on the World Wide Web
at:
http://amesnews.arc.nasa.gov/releases/2002/02images/microwaveplants/microwaveplants.html
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